Respiratory System: Ventilation and Gas Exchange

Key Terms

• Ventilation includes inhalation and exhalation.
• Respiration includes external and internal respiration.
• Perfusion refers to blood flow.

Structure and Function of the Respiratory System

• Nose: Filters, warms, and moisturizes the air.
• Pharynx: The epiglottis opens when air enters.
• Larynx: Air flows through it, allowing sound and vocals to be heard.
• Trachea: A strong, flexible tube that filters and delivers air to the lungs.
• Bronchi: The division of the trachea that leads to each lung.
• Bronchioles: Smaller branches of the bronchi.
• Alveoli: Small air sacs where gas exchange occurs.

Introduction to Gas Exchange

• Gas exchange is vital for maintaining homeostasis.
• Oxygen is needed to produce energy, so it has to reach cells
• Carbon dioxide must be removed from the body during gas exchange.
• Respiration includes the gases exchange in the lungs and the tissues.

How Gas Exchange Occurs

• Diffusion principles determine if O2 or CO2 enters or exits the blood in the lungs and tissues.
• Gases exert pressure, the amount is called partial pressure, symbolized as PO2 and PCO2.
• Oxygen diffuses from higher to lower partial pressure when partial oxygen pressure varies across a membrane.

Theory of Diffusion and Respiration

• Diffusion: Molecules move from a high to a low concentration gradient.
• Gas exchange process: Molecules move from high to low concentration.
• Equilibrium is is reached when concentration is equal in both sides of a membrane

Factors Affecting Diffusion Rate

• Surface area: Diffusion increases as surface area increases (directly proportional).
• Concentration gradient: Diffusion is faster with a greater concentration gradient (directly proportional).
• Thickness of gas exchange surface: Thicker surfaces lead to slower diffusion (inversely proportional).
• Temperature: Higher temperatures increase diffusion rate (directly proportional).

Respiratory Membrane

• The alveoli walls consist of a Type I Alveoli cell layer.
• The alveoli are surrounded by pulmonary capillaries.

External Respiration

• Refers to gas exchange between air in the alveoli and blood in the pulmonary capillaries.
• Blood in pulmonary capillaries has a higher PCO2 than atmospheric air.
• CO2 diffuses out of the plasma into the lungs.
• Most CO2 is carried in plasma as bicarbonate ions (HCO3 −).

Internal Respiration

• Refers to gas exchange between blood in systemic capillaries and tissue cells.
• Blood entering capillaries is a bright red because of oxyhemoglobin in red blood cells.
• Tissues have a higher temperature and a lower pH, so oxyhemoglobin gives up oxygen.
• then diffuses out of the blood into the tissues.

Physiology

• Mechanism: Can also be referred to as Ventilation – Perfusion.
• Ventilation (V): The flow of air into and out of the alveoli.
• Inhalation: higher atmospheric pressure than alveolar pressure.
• Exhalation: lower atmospheric pressure than alveolar pressure.
• Perfusion (Q): The flow of blood to alveolar capillaries.
• Ventilation/Perfusion (V/Q) ratio:
• Optimal gas exchange needs balances ventilation(V) and perfusion(Q) to achieve optimal gas exchange.
• Ventilation of Alveoli (V): 4 Liters/min
• Cardiac output = Perfusion at Alveoli (Q): 5 Liters/min
• V/Q ratio = (4 L/min) / (5 L/min) = 4/5, or 0.8 for the entire lung.

Pathophysiology

• Optimal V/Q ratio = 0.8
• Regional differences in ventilation and perfusion are theoretically possible.
• There is perfusion is gravity depended.
• Ventilation-perfusion mismatch: Ventilation and perfusion mismatched distributions, with disproportionately high ventilation in some lung units and disproportionately high perfusion in others.
• Better V/Q match in 'bad lung up' position due to greater perfusion in dependent areas.
• V/Q commonly mismatched if affected lung is dependent.

Internal vs. External Respiration

• Internal respiration: Occurs in body tissues; cells release carbon dioxide and take in oxygen from blood.
• External respiration: Occurs in the lungs, body takes in oxygen from atmosphere and releases carbon dioxide.

Physiology of O2 Transport

• Via Plasma:
• O2 is less than 2%.
• Via Hemoglobin:
• The hemoglobin molecule has four binding sites for oxygen molecules.
• Hemoglobin's ability to take and release oxygen depends on the amount of oxygen in the surrounding tissue.
• There are iron atoms in the four heme groups.
• Each Hb can bind four oxygen molecules.

O2 Transport at Tissue Level

• At low PO2 is difficult for O2 associate with the Heme groups.
• Conformational changes and 02 binding occur when one heme group becomes occupied with oxygen and oxygen becomes favored.
• In lungs at high PO2 the hemoglobin binding sites are occupied
• More 02 displaces the hemogloibin in presence of CO2
• More 02 is realsed into tissue as an effect

Physiology of CO2 Transport

• Via Plasma: 5%
• Via Hemoglobin: 10% of hemoglobin combine directly with the hemoglobin binding cites.
• Via Blood Plasma: 85% transported via bicarbonate ions

Oxygen Unloading

• Bohr Shift occurs where there are high CO2 concentrations in tissues.
• H+ binds with hemoglobin and returns oxygen to the tissues.
• This process needed to create aerobic metabolism.

Pathophysiology of Respiration

• Haldane Effect: The degree to which CO2 transported in the blood is affected by how much blood is oxygenated, lower Hb saturation with O2, and more CO2 the blood can carry.
• Hypoxemia: low blood oxygen levels (measured by Oximeter).
• Hypoxia: low tissue oxygen levels. (measured by ABG).

Explore the key components of the respiratory system, including the nose, pharynx, larynx, trachea, bronchi, and alveoli. Learn about gas exchange, focusing on oxygen uptake and carbon dioxide removal. Understand the roles of ventilation, respiration, and perfusion in maintaining homeostasis.